Processing of clay



United States Patent US. Cl. 209 4 Claims ABSTRACT OF THE DISCLOSURE Amethod of removing titanium mineral impurities from a clay containing atleast 40% by weight of particles smaller than 2 microns equivalentspherical diameter which comprises conditioning the clay at a solidscontent of at least 30% by weight for a time suflicient to dissipatetherein at least 25 horsepower hours of energy per ton of solids andthereafter subjecting the clay to a froth flotation process in thepresence of an activator consisting of a water-soluble salt of analkaline earth metal or a heavy metal.

BACKGROUND OF THE INVENTION This is a continuatiou-in-part ofapplication Ser. No. 435,340 filed Feb. 25, 1965 and now abandoned.

This invention relates to the processing of clays, of which kaolin andchina clay are examples, containing at least 40% by Weight of particlessmaller than 2 microns equivalent spherical diameter, and is moreparticularly concerned with a method of treating such clays to improvethe brightness thereof by removing titanium mineral impuritiestherefrom.

Titanium mineral impurities occur in some clays as mined and, if theyare colored, they detract from the appearance of the clay. It haspreviously been proposed to remove impurities by forming a suspension,or slurry, raising the pH of the slurry of the clay to an alkalinevalue, for example by the addition of ammonium hydroxide, and subjectingthe slurry to a froth flotation process. In general the froth flotationprocess comprises adding a collector, for example oleic acid, to thealkaline slurry of the clay, conditioning the slurry by agitating theslurry in a tank for a time suflicient to dissipate therein about 5 tohorsepower hours of energy per ton of solids, adding a frothing agent,for example pine oil, to the conditioned slurry, and then passing airthrough the slurry in a known manner in a froth flotation cell to effectseparation of the impurities from the clay. However, many claysnaturally contain a high proportion, i.e. greater than 40% by weight, ofparticles of extremely small dimensions, i.e. two microns equivalentspherical diameter or smaller, and these clays are therefore naturalslirnes; such particles are difficult to separate by a simple frothflotation process of the type described above. The individual, extremelysmall particles of the clay are grouped together into large masses andare loosely bound by inter-particulate forces i.e. they are flocculated.Such masses may have impurities included and held therein and theseimpurities, which are bound in the larger masses, are not thereforecapable of being separated by a simple froth flotation process. In fact,in many industrial froth flotation processes, all the materialconsisting of particles smaller than 50 microns is separated from thecrude ore and discarded. In order to try to overcome this problem it hasbeen proposed to deflocculate the clay before treating the same by afroth flotation process. To effect the deflocculation, it has beenproposed to add, for example, sodium silicate to the clay slurry beforethe addition of the ammonium hydroxide.

It has also been proposed to add an activator to the slurry beforecarrying out the froth flotation process, see for example United StatesPatent No. 2,894,628 in which it is proposed that the froth flotationprocess described above should be carried out in the presence of anactivator selected from ammonium, potassium and magnesium sulphates.However, all of these \known processes only work efficiently with coarseclays, i.e. clays containing not more than by weight of particlessmaller than 2 microns, and do not work efficiently with clayscontaining a high proportion, i.e. greater than 40% by weight, ofparticles smaller than 2 microns equivalent spherical diameter.

SUMMARY OF Til-IE INVE'N'IIION I have now discovered that thedifliculties which arise when attempting to refine by a froth flotationprocess clays containing more than 40% by Weight of particles smallerthan 2 microns equivalent spherical diameter are, to a large extent, duetosurface contamination of the particles which reduces the effectivedifference between two different mineral particles. To overcome thesedifliculties I propose, in accordance with the present invention, tosubject the particles toa thorough scrubbing prior to carrying out thefroth flotation process and to carry out the froth flotation process inthe presence of an activator which is a Water-soluble salt of analkaline earth metal or a heavy metal. More particularly, according tothe present invention there is provided a method of treating a claycontaining at least 40% by Weight of particles smaller than 2 micronsequivalent spherical diameter in order to separate therefrom titaniummineral impurities, which method comprises the steps of:

'(a) Mixing the clay in the form of an aqueous slurry having a solidscontent of at least 30% by weight with an alkali to raise the pH of saidaqueous slurry to an alkaline value, a deflocculant, a collector for thetitanium mineral impurities, and an activator consisting of awater-soluble salt of a metal chosen from the alkaline earth metals andthe heavy metals;

'(b) Conditioning the clay slurry at said solids content of at least 30%by Weight for a time suflicient to dissipate therein at least 25horsepower hours of energy per ton of solids;

(c) Adding to the conditioned clay slurry a frothing agent; and

((1) Introducing the conditioned clay slurry containing the frothingagent into a froth flotation cell and subjecting the conditioned clayslurry to a froth flotation process.

Herein the term alkaline earth metals is to be understood to includemagnesium, and the term heavy metals refers to metals having a specificgravity which is greater than 4.

DESCRIPTION OF THE PREFERRED EMBODIMENTS To accomplish the thoroughscrubbing of the particles before carrying out the froth flotationprocess, it is essential that the conditioning of the clay slurry becarried out before the frothing agent is added thereto and at a solidscontent of at least 30% by weight. However, it is preferred that thesolids content of the aqueous clay slurry be in the range of from 40% to60% by weight.

The activator, which is a water-soluble salt of an alkaline earth metalor a heavy metal, is advantageously a water-soluble salt of barium,calcium, cupric copper, ferrous iron, plumbous lead, magnesium,manganous manganese, strontium or zinc. Examples of suitable salts arelead acetate, lead nitrate, barium chloride and calcium chloride. Theamount of activator employed is generally in the range of from 0.2 to2.0 lbs. per ton of solids in the clay slurry.

The alkali used for raising the pH of the slurry to an alkaline valuecan be ammonium hydroxide although it will be appreciated that othersimilar materials may alternatively be used.

The deflocculant can be, for example, sodium silicate.

The collector for the titanium mineral impurities can be, for example,oleic acid, and the frothing agent can be, for example, pine oil.

After the clay slurry has been conditioned and before it is treatedinthe froth flotation cell it is advantageously diluted with water to asolids content of from 15 to 20% by weight.

The whole of the necessary quantities of the activator and of thecollector are not necessarily added to the aqueous slurry of the claybefore the beginning of the froth flotation process. Indeed, it has beenfound advantageous to add about one half the required quantity of eachof these reagents prior to initiating the froth flotation process; and,thereafter, during the froth flotation process, to add further, smallerquantities of collector and activator, there preferably being a periodof conditioning of the aqueous slurry of the clay after each furtheraddition of reagent.

In order that the invention may be more clearly understood and readilycarried into effect, reference will now be made to the followingexample.

Example In this example, a sample of kaolin from Georgia, United Statesof America, was employed. The chosen sample contained 45% by weight ofparticles smaller than 2 microns equivalent spherical diameter andshowed a relatively high coloration. The clay was formed into an aqueousslurry having a solids content of 40% by weight. Sodium silicate wasthen added to the suspension in the amount of approximately 4 lbs. ofsilicate per ton of clay in order to deflocculate the clay. The slurrywas then partially conditioned by agitation for 6 minutes with ahigh-speed stirrer. After the agitation, lead acetate, as activator, wasadded in the amount of 1.25 pounds per ton of clay, followed by 10%ammonium hydroxide solution in the amount of 2 pounds per ton and oleicacid in the amount of 3 pounds per ton of clay. The resulting clayslurry was further conditioned for a period of 6 minutes with thehigh-speed stirrer. The use of the high-speed stirrer and the totalconditioning time of 12 minutes at the high solids content means thatthere was dissipated in the clay slurry about 30 horsepower hours ofenergy per ton of solids. After being conditioned, the clay slurry wasdiluted to form a slurry having a solids content of 16%. The resultingdiluted slurry was treated in a froth flotation cell after the additionof pine oil as a frothing agent. At intervals of 20 to 25 minutes,further quantities of lead acetate and oleic acid were added at from Ato A2 of the original amount, each addition being followed by aconditioning period before restarting the froth flotation process. Thetotal time of the froth flotation process was about 100 minutes.

The total consumption of reagents per ton of clay was as follows:

Lbs. Oleic acid 6.75 Ammonium hydroxide 2 Lead acetate 2.5 Sodiumsilicate 4 To determine the degree of purification of the clay,brightness values were measured both for the original clay and for theproduct of the process just described. The brightness of the clay wasdetermined by measuring the percentage reflectance of violet lighthaving a wave length of 458 millimicrons. The results of the tests aregiven in the table below. The clay treated by the process just describedwill for brevity be referred to as Clay A.

For comparison purposes, two separate samples of clay were processed byknown methods. The first sample was formed into a slurry, conditionedfor a time sufficient to dissipate therein about 10 horsepower hours ofenergy per ton of solids and treated with ammonium hydroxide to raisethe pH level to pH 9; a froth flotation process was then carried out inknown manner, using oleic acid as a collector and pine oil as a frothingagent. The clay treated by this method is referred to as Clay B in thetable below. The second sample of comparison clay, Clay C, was treatedin the same way as was Clay B except that sodium silicate was addedbefore alkalination to ensure substantially complete deflocculation ofthe clay in the suspension.

I claim:

1. A method of treating a clay to remove therefrom titanium mineralimpurities, said method comprising the steps of:

(a) mixing a clay containing at least 40% by weight of particles smallerthan 2 microns equivalent spherical diameter in the form of an aqueousslurry having a solids content of clay of at least 30% by weight with analkali to raise the pH of said aqueous clay slurry to an alkaline value,a deflocculant, a collector for the titanium mineral impurities, and anactivator consisting of a water-soluble salt of a metal chosen from thealkaline earth metals and the heavy metals;

(b) conditioning the aqueous clay slurry at said solids content of atleast 30% by weight for a time suflicient to dissipate therein at least25 horsepower hours of energy per ton of solids;

(0) adding to the conditioned aqueous clay slurry a frothing agent; and

(d) introducing the conditioned aqueous clay slurry containing thefrothing agent into a froth flotation cell and subjecting theconditioned aqueous clay slurry to a froth flotation process.

2. A method according to claim 1, wherein the aqueous clay slurry isconditioned at a solids content of clay of from 40% to 60% by weight.

3. A method according to claim 2, wherein the conditioned aqueous clayslurry is diluted to a solids content of clay of from 15% to 20% byweight before it is subjected to a froth flotation process.

4. A method according to claim 1 wherein the heavy metal has a specificgravity greater than 4.

References Cited UNITED STATES PATENTS 1,029,579 6/ 1912 Schwerm 209-52,105,826 1/1938 Tartaron 209-166 2,249,569 7/1941 Phelps 209-1662,249,570 7/ 1941 Lane 209-166 2,569,680 10/1951 Leek 209-10 2,661,84212/1953 Duke 209-166 2,861,687 11/ 1958 Lord 209-167 2,894,628 7/ 1959Duke 209-166 3,164,549 1/1965 Seymour 209-166 2,990,958 7/1961 Greene209-166 3,224,582 12/1965 Iannicelli 209-166 3,337,048 8/1967 Mercade209-5 3,353,668 11/1967 Duke 209-166 X HARRY B. THORNTON, PrimaryExaminer.

ROBERT HALPER, Assistant Examiner.

US. Cl. X.R. 209-166

